Re: Materials/parts...

[Phil Nuytten <72020.572@compuserve.com>]

Hi, Gene:
 Sure, If you use a short section of a cylinder with an attatched head as
your 'conning tower' or entry hatch ( the hatch ring is set into the head)
then the stress levels at the right angle portion of the weld joining this
vertcal cylinder/hd to the horizontal hull are very high . .but, if you
think about the shape of the joining cut on the vertical tank ( and
presuming it is the same size cylinder as the horizontal hull or close)
then you can see that there is a right angle between these pieces only at
trhe 12 o'clock position ( if you were to consider a section through the
horizontal hull) and that angle decrease as as you approach the midline of
the horizontal tank - and vanishes at the 9 o'clock and 3 o'clock position
. .which is, effectively, the ends of your vertical. In other words, the
stress caused by pressure will be highest  at the top center (12 o'clock)
and will diminish as the angle decreases until it is no greater than any
other area of hull stress  . . phew! . .,bear  with me, here . . .if you
make up a plate that is shaped like an old-fashioned horse-collar, with the
inside curve the same as the lines of the weld and the outside curve, say,
six inches higher, but tapering to zero difference at each end . .this
piece is 'stood-up' on the line of the weld halfway between the vertical
line of the entry cylinder and the horizontal line of the hull cylinder, it
will act as an external stiffener, giving maximum stiffness where it is the
widest ( 6") and the weld stress the highest ( 12 o'clock) and tapering off
to to no stiffener as the stress tapers to normal. Two of these plates are
required, one in front of the vertcal cylinder and one aft. Gee, would take
about five seconds to explain with a pencil! (G) Using this system and also
extending the vertical cylinder into the horizontal cylinder a few inches (
2 or 3) to act as a tee stiffener ( istead of simply butting these sections
together), you can get away without a hatch area doubler plate - which
would have to be rolled, otherwise- all of this, of course, providing that
that the depth/pressure that you wish toachieve is conservatively do-able
with the hull diameter and material thickness that you plan to use.
        I suspect that most of you will go for a given, available, tank and
say "OK. how deep will this get me, safely and how do I get in and out and
how do I put in viewports and penetrator plates?" I really should get off
my ass and post a simple table that shows hull diameters vs lengths and the
different collapse and safe working depths for typical mild steel
hulls/tanks of various thicknesses. Most people, are unaware, for example,
of the degree to which diameter effects working depth for a given
thickness, ( almost exponential!) or the effect of increasing/decreasing
unsupported hull length (or the span between heads) or why the heads can
often be half the thickness or less, of the cylindrical portion of the hull
. . .but, I drone on... Good luck !

Regards,
Phil